1. Field of the Invention
The present invention relates to a process for metal-plating a resin molded article formed from a resin composition containing as main components a polyphenylene sulfide and a glass-reinforcing agent(filler), particularly to a process of pretreatment of metal-plating. More detailedly, the invention relates to a process which comprises pretreating the above resin molded article and then metal-plating the resultant resin molded article to obtain a resin molded article having a strong peel strength of the metal plated layer as well as an excellant smoothness of the surface, and to the obtained molded article.
2. Prior Art
Polyphenylene sulfide (hereinafter sometimes abbreviated as "PPS") is known as a resin excellent in heat resistance, solvent resistance, electric characteristics, mechanical strength, dimensional stability, flame retardancy, etc., and has recently received attention. Particularly, this PPS resin can further be improved in the above performances by conjugation with a fibrous reinforcing agent such as glass fiber and carbon fiber or with an inorganic filler such as talc, clay and silica, and the resultant improved resins are widely used as electric parts, electronic parts, mechanical structural parts, etc. On the other hand, based on its excellent solder heat resistance, dielectric characteristic and the like, use development of PPS resin as a material for printed circuit boards, three dimensional molded printed circuit boards has also been progressed. It is considered that metal plating is indispensable for PPS resin molded articles to be utilized for these uses. However, since the PPS resin is excellent in chemicals resistance, it is extremely difficult to chemically etch it and when metal-plating is made, it is difficult to obtain a sufficient peel strength of the metal. Thus, there has been developed and proposed treating liquids for chemically etching, before metal plating, molded articles of PPS resins or reinforced PPS resin compositions. Namely, various processes have been proposed which comprise etching a molded article of a PPS resin or glass reinforcing agent-containing PPS resin for its surface with nitric acid alone, a mixed liquid of nitric acid and hydrofluoric acid, a solution of hydrofluoric acid or a solution of ammonium hydrogenfluoride or a mixed liquid of nitric acid and a fluoride salt, and then metal plating the etched molded article to obtain a plated molded article having an excellent adhesive strength (Japanese Laid-Open Patent Publications Nos. 54290/1984, 63674/1987, 142786/1987 and 14880/1988).
According to these known processes, the present inventors etched a molded article of a glass reinforcing agent particularly glass fiber-containing PPS resin with a mixed liquid of nitric acid and hydrofluoric acid (or its salt) and then metal plated the resulting etched molded article. As a result, it was revealed that a severe treatment is necessary to obtain a sufficient peel strength by this etching and as a result, unevenness of the plated surface becomes extremely large and appearance thereof also becomes bad. When a plated product is used in preparation of a printed circuit board by resist pattern formation, electric plating or the like or a three dimensional molded printed circuit board, it has become a large obstacle and practical problem that unevenness of the plated surface is thus large and surface smoothness is insufficient.